568 THE FRESH- WATER LOCHS OF SCOTLAND 
flat chalky surfaces surrounded with sand — and therefore all the traflic 
routes pass through them. 
Lake Ngami^ is the central point of an inland water-system of South 
Africa, in lat. 20^° S., long. 23° E., at an altitude of about 3000 feet 
aboye sea-level. The lake was once 20 miles long and 10 miles wide, 
but is now dry, consisting merely of an expanse of reeds growing in a 
soft, treacherous soil, below which brackish water is found at a depth 
of 20 feet. The former feeder of the lake was the Taukhe or Tiohge 
River (known in the upper part of its course as the Okavango or 
Cubango River), which entered at the north-west end, but now a 
portion at least of its vraters passes by a channel north of Lake 
Ngami into the Botletle or Zuga River, by which the overflow of 
the lake was formerly carried off' eastwards at the time of high 
water. The Botletle River loses itself in a system of salt-pans — 
round or oval basins of varying size sunk to depths of 30 to 45 feet 
in the sandstone, and often bounded by steep banks. The largest 
of these is the salt-pan called Makarri karri. The outer pans are dry 
for a large part of the year, the whole system being filled only at 
the height of the flood season in August. 
The lowest twenty miles of the Taukhe River are said to have been 
dry since about 1890, the district intersected by the river-beds now 
growing corn in great plenty. The cessation of the river's flow was 
caused, according to native report, by a blocking of the channel by 
thousands of rafts, on which the Makoba natives brought down their 
yearly tribute of corn. 
Precipitation is greater in Northern Kalahari than in the 
southern and central portions. In the former the river-courses are 
marshy even in the dry season. Flooded plains still hold a little 
w^ater at the end of the dry season, and sand -pans with permanent 
ponds are not uncommon. In Southern and Central Kalahari the 
salt-pans contain water only in the rainy season ; at other times they 
drv up and leave behind a crust of salt. 
Underground water does not exist to any extent in the Kalahari 
as in the Sahara. In the dry regions the scanty rainfall is absorbed 
by the sand, and evaporates in the long dry season ; in the alluvial 
regions underground water is comparatively small in quantity, for 
the steep crumbling ground-rock does not form a good water-way. 
The inland drainage areas of South America are estimated by 
Murray at over 500,000 square mUes (see fig. 69). 
According to Neveu-Lemaire,^ the region of South America lying 
1 See Encijd. Brit., eel. 10, vol. xxxi. p. 228 ; see also note on Dr Poch's ex- 
pedition, Geogr. Jour?i., vol. xxxiii. p. 601, 1909. 
2 See " Le Titicaca et le Poopo," La Geographie, vol. ix. p. 409, 1904. 
